1. Technical Field
The present invention relates to a semi-transmissive reflective liquid crystal device which includes a layer thickness adjustment film for defining the thickness of a liquid crystal layer in a reflective display region and an electronic apparatus using the liquid crystal device.
2. Related Art
Currently, a liquid crystal device is widely used in electronic apparatuses such as mobile telephones or personal digital assistants (PDA). For example, the liquid crystal device is used as a display device for displaying information on the electronic apparatus. The liquid crystal device controls a voltage applied to a liquid crystal layer provided between a pair of substrates for each pixel, controls alignment of liquid crystal molecules in the liquid crystal layer for each pixel, modulates polarized light transmitting through the liquid crystal layer for each pixel, and displays an image on the surface of any one of the substrates.
In the related art, a semi-transmissive reflective liquid crystal device is known (for example, see JP-A-2005-338256 (page 6, FIG. 2)). In this liquid crystal device, a reflective display region is formed by a common wiring line functioning as a reflective plate, a transmissive display region is formed by a region in which the common wiring line is not provided, and a reflective display and a transmissive display are selectively performed by selectively applying driving voltages to electrodes in these regions.
In the liquid crystal device disclosed in JP-A-2005-338256, light transmitting through the transmissive display region transmits through the liquid crystal layer one, but light transmitting through the reflective display region transmits through the liquid crystal layer twice. Accordingly, a difference in retardation (Δnd: Δn is a refractive index phase difference and d is the thickness of the liquid crystal layer) occurs by the reflected light and the transmitted light so as to make the display characteristics of the reflective display and the transmissive display ununiform. In order to compensate for the difference in retardation, in the liquid crystal device disclosed in JP-A-2005-338256, a built-in retardation film is provided in the reflective display region as a layer thickness adjustment film for adjusting the thickness d of the liquid crystal layer.
The liquid crystal device disclosed in JP-A-2005-338256 is an in-plane field type liquid crystal device in which a pixel electrode and a common electrode are formed on a substrate and the built-in retardation film is provided on a substrate which faces the substrate, on which the electrodes are formed, as the layer thickness adjustment film. The liquid crystal molecules of the liquid crystal layer are aligned in homogeneous alignment by rubbing alignment films provided on a pair of substrates.
The layer thickness adjustment film has a step difference surface at a boundary between the reflective display region and the transmissive display region, and the step difference surface is a sloped surface. This sloped surface is formed when the layer thickness adjustment film is formed using a photolithography method. In liquid crystal device disclosed in JP-A-2005-338256, the step difference surface of the layer thickness adjustment film extends perpendicular to a signal wiring line. In JP-A-2005-338256, several examples of an angle between the extending direction of the step difference surface of the layer thickness adjustment film and a rubbing direction for aligning the liquid crystal molecules are described and, among them, the extending direction of the step difference surface and the rubbing direction are 75° or 90°. However, an orientation relationship between the rubbing direction and the step difference surface, that is, whether the rubbing process is performed in a direction opposed to the step difference surface or from a mountain portion to a valley portion of the step difference surface, is not disclosed.
The present inventors found that, if the orientation relationship is not adequately set, a sufficient alignment force cannot be obtained in the step difference surface of the layer thickness adjustment film, the alignment of the liquid crystal molecules is disturbed, and contrast deteriorates due to the disturbance of the alignment, through an experiment for the orientation relationship between the step difference surface of the layer thickness adjustment film and the rubbing direction.